7.1 Overview

The LMT89 device is a precision analog output CMOS integrated-circuit temperature sensor that operates over a temperature range of −55°C to 130°C . The power supply operating range is 2.4 V to 5.5 V. The transfer function of LMT89 is predominately linear, yet has a slight predictable parabolic curvature. The accuracy of the LMT89 device, when specified to a parabolic transfer function, is typically ±1.5°C at an ambient temperature of 30°C. The temperature error increases linearly and reaches a maximum of ±5°C at the temperature range extremes. The temperature range is affected by the power supply voltage. At a power supply voltage of 2.7 V to 5.5 V, the temperature range extremes are 130°C and −55°C. Decreasing the power supply voltage to 2.4 V changes the negative extreme to −30°C, while the positive remains at 130°C.

The LMT89 quiescent current is less than 10 μA. Therefore, self-heating is less than 0.02°C in still air. Shutdown capability for the LMT89 is intrinsic because its inherent low power consumption allows it to be powered directly from the output of many logic gates or does not necessitate shutdown at all.

The temperature sensing element is comprised of a simple base emitter junction that is forward biased by a current source. The temperature sensing element is then buffered by an amplifier and provided to the OUT pin. The amplifier has a simple class A output stage thus providing a low impedance output that can source 16 µA and sink 1 µA.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 LMT89 Transfer Function

The transfer function of the LMT89 device can be described in different ways with varying levels of precision. A simple linear transfer function with good accuracy near 25°C is shown in Equation 1.

Equation 1. V_O = −11.69 mV/°C × T + 1.8663 V

Over the full operating temperature range of −55°C to 130°C, best accuracy can be obtained by using the parabolic transfer function.

Equation 2. V_O = (−3.88 × 10⁻⁶ × T²) + (−1.15 × 10⁻² × T) + 1.8639

Using Equation 2 the following temperature to voltage output characteristic table can be generated.

Table 1. Temperature to Voltage Output Characteristic Table

TEMP (°C)	VOUT (V)	TEMP (°C)	VOUT (V)	TEMP (°C)	VOUT (V)	TEMP (°C)	VOUT (V)	TEMP (°C)	VOUT (V)	TEMP (°C)	VOUT (V)	TEMP (°C)	VOUT (V)
–55	2.4847	–28	2.1829	–1	1.8754	26	1.5623	53	1.2435	80	0.9191	107	0.5890
–54	2.4736	–27	2.1716	0	1.8639	27	1.5506	54	1.2316	81	0.9069	108	0.5766
–53	2.4625	–26	2.1603	1	1.8524	28	1.5389	55	1.2197	82	0.8948	109	0.5643
–52	2.4514	–25	2.1490	2	1.8409	29	1.5271	56	1.2077	83	0.8827	110	0.5520
–51	2.4403	–24	2.1377	3	1.8294	30	1.5154	57	1.1958	84	0.8705	111	0.5396
–50	2.4292	–23	2.1263	4	1.8178	31	1.5037	58	1.1838	85	0.8584	112	0.5272
–49	2.4181	–22	2.1150	5	1.8063	32	1.4919	59	1.1719	86	0.8462	113	0.5149
–48	2.4070	–21	2.1037	6	1.7948	33	1.4802	60	1.1599	87	0.8340	114	0.5025
–47	2.3958	–20	2.0923	7	1.7832	34	1.4684	61	1.1480	88	0.8219	115	0.4901
–46	2.3847	–19	2.0810	8	1.7717	35	1.4566	62	1.1360	89	0.8097	116	0.4777
–45	2.3735	–18	2.0696	9	1.7601	36	1.4449	63	1.1240	90	0.7975	117	0.4653
–44	2.3624	–17	2.0583	10	1.7485	37	1.4331	64	1.1120	91	0.7853	118	0.4529
–43	2.3512	–16	2.0469	11	1.7369	38	1.4213	65	1.1000	92	0.7731	119	0.4405
–42	2.3401	–15	2.0355	12	1.7253	39	1.4095	66	1.0880	93	0.7608	120	0.4280
–41	2.3289	–14	2.0241	13	1.7137	40	1.3977	67	1.0760	94	0.7486	121	0.4156
–40	2.3177	–13	2.0127	14	1.7021	41	1.3859	68	1.0640	95	0.7364	122	0.4032
–39	2.3065	–12	2.0013	15	1.6905	42	1.3741	69	1.0519	96	0.7241	123	0.3907
–38	2.2953	–11	1.9899	16	1.6789	43	1.3622	70	1.0399	97	0.7119	124	0.3782
–37	2.2841	–10	1.9785	17	1.6673	44	1.3504	71	1.0278	98	0.6996	125	0.3658
–36	2.2729	–9	1.9671	18	1.6556	45	1.3385	72	1.0158	99	0.6874	126	0.3533
–35	2.2616	–8	1.9557	19	1.6440	46	1.3267	73	1.0037	100	0.6751	127	0.3408
–34	2.2504	–7	1.9442	20	1.6323	47	1.3148	74	0.9917	101	0.6628	128	0.3283
–33	2.2392	–6	1.9328	21	1.6207	48	1.3030	75	0.9796	102	0.6505	129	0.3158
–32	2.2279	–5	1.9213	22	1.6090	49	1.2911	76	0.9675	103	0.6382	130	0.3033
–31	2.2167	–4	1.9098	23	1.5973	50	1.2792	77	0.9554	104	0.6259	—	—
–30	2.2054	–3	1.8984	24	1.5857	51	1.2673	78	0.9433	105	0.6136	—	—
–29	2.1941	–2	1.8869	25	1.5740	52	1.2554	79	0.9312	106	0.6013	—	—

Solving Equation 2 for T:

Equation 3.

For other methods of calculating T, see Detailed Design Procedure.

7.4 Device Functional Modes

The only functional mode of the LMT89 device is that it has an analog output inversely proportional to temperature.